 #define _CRT_SECURE_NO_WARNINGS 1

// 滚动数组优化 
class Solution {
	
public:
	int tribonacci(int n) {
		if (n == 0) return 0;
		if (n == 1 || n == 2) return 1;
		int a = 0, b = 1, c = 1, d = 0;
		for (int i = 3; i <= n; i++)
		{
			d = a + b + c;
			a = b; b = c; c = d;
		}
		return d;
	}
};